SCHN_STAT_CHAIN_CHECK
backed_up = scsw_cstat(&request->irb.scsw) & SCHN_STAT_CHAIN_CHECK;
request->irb.scsw.cmd.cstat &= ~SCHN_STAT_CHAIN_CHECK;
SCHN_STAT_CHN_DATA_CHK | SCHN_STAT_CHAIN_CHECK |